Brachiopod Assemblages Research Articles

Brachiopod faunas, facies and biostratigraphy of the Pridolian to lower Eifelian succession in the Rhenish Massif (Rheinisches Schiefergebirge, Germany)

Abstract The succession of Pridolian to lower Eifelian (uppermost Silurian to lowermost Middle Devonian) rhynchonelliformean brachiopod faunas from the Rhenish Massif (Germany) is described and interpreted against the background of sedimentary sequences and facies development. The predominant rhenotypic (‘Rhenish’) facies is redefined as a neritic-siliciclastic facies type of the Devonian. It is subdivided into eurhenotypic, pararhenotypic and allorhenotypic subfacies, based on sedimentary features and specific brachiopod assemblages reflecting different shallow-marine palaeoenvironments under more or less terrigenous influence. The studied sedimentary successions are subdivided biostratigraphically on the basis of brachiopods, correlated on a supraregional scale, and calibrated in terms of the global chronostratigraphy. Stratigraphic intervals with characteristic brachiopod faunas are distinguished. Faunal turnovers between these are attributed to regional events in the context of short or more extended phases of palaeoenvironmental change presumably caused mainly by sea-level fluctuations in combination with varying crustal subsidence and sedimentation rates. These changes resulted in shelf-wide or more regional extinction or emigration of substantial parts of a brachiopod fauna and subsequent replacement by a largely new one. Finally, new taxa of brachiopods are introduced: Sartenaerirhynchus gen. nov., Paraspirifer ( Mosellospirifer ) subgen. nov., Paraspirifer ( Laurentispirifer ) subgen. nov., Iridistrophia ( Flabellistrophia ) subgen. nov. and Iridistrophia ( Flabellistrophia ) musculosa sp. nov.

Similarity of Early and Middle Jurassic brachiopods between the Danubian and Getic tectonic units of eastern Serbia

Rich brachiopod assemblages are known from the Lower and Middle Jurassic deposits of the Danubian and Getic tectonic units (eastern Serbia). A quantitative assessment of the relevant palaeontological data can shed light on the relationship of these units in the palaeospace. In the present study, the brachiopod assemblages from the Danubian and Getic tectonic units are compared with similarity indices (the Jaccard similarity of species, genera, families, and superfamilies, and the Czekanowski and Gower similarity of the genus–species, family–species, and superfamily-species diversity structures). This analysis is applied to five geological time slices when brachiopods flourished regionally, namely the Early Pliensbachian, the Late Bajocian, the Early Bathonian, the Middle Bathonian, and the Late Bathonian. Generally, the values of the indices imply moderate similarity. The similarity was significantly lower in the Middle Jurassic relatively to the Early Jurassic. The similarity of the Early Pliensbachian brachiopods of the Danubian and Getic tectonic units was significant relatively to the similarity between some European regions. The documented decrease in the similarity through the geological time can be explained by the increase in the global palaeobiogeographical differentiation in the Middle Jurassic.

Patterns of brachiopod faunal and body-size changes across the Permian−Triassic boundary: Evidence from the Daoduishan section in Meishan area, South China

New analysis of Permian–Triassic brachiopod assemblages and body-size changes in South China provides insights into the process of the environmental crisis in the lead up to the end-Permian mass extinction. The recently discovered Daoduishan section of South China can be considered as an important auxiliary section for the study of brachiopods at the Meishan Section D of South China, the GSSP of the Permian–Triassic Boundary (PTB). This paper studied changes of the brachiopod assemblages and body sizes through the upper part of the Changxing Formation and basal Yinkeng Formation of Daoduishan. The results show that significant changes of brachiopod assemblages took place between Beds 24e and 26. Brachiopods?Prelissorhynchia sp. and Paracruirithyris pygmaea are the dominators in Beds 14–24e, while Tethyochonetes pigmaea and Paryphella spp. are the dominators in Beds 26–29. Body sizes of brachiopods significantly decreased between Beds 24e and 26 and then maintained smaller means in Beds 27–29. Studies of brachiopod morphological features indicate both Tethyochonetes and Paryphella had advantageous adaptations enabling them to copy with living in an anoxic/dysoxic and/or low-productivity environment during the Permian–Triassic crisis.

Comparative study of Late Devonian (Famennian) brachiopod assemblages, sea level changes, and geo-events in northwestern and southern China

Abundant brachiopods have been recovered from the Upper Devonian of western Junggar, Xinjiang, northwestern China. However, their diversity and succession, as well as a detailed comparison with other regions, remain to be explored. These issues are of importance since conodonts and ammonoids are generally sparse for dating the sequence. Based on collections in the past years from the Famennian sequence of the Bulongguoer section and adjacent sections, we recognize five brachiopod assemblages in ascending order: the Caenanoplia? aff. logani Assemblage; the Palaeospirifer–Megalopterorhynchus Assemblage, which can be divided into the Cyrtospirifer sulcifer Subassemblage and the Rugaltarostrum Subassemblage; the Ambocoelia? cf. unionensis Assemblage; the Austrospirifer? sp. Assemblage; and the Syringothyris–Spirifer Assemblage. Comparison of these assemblages with those of the Xikuangshan and other sections, central Hunan, southern China, indicates a strong biogeographic differentiation. There are opposite trends of raw diversity changes during the middle Famennian in these two regions, whereas similar trends, with a decline followed by an increase in diversity, occurred during the late and latest Famennian. Two transgression–regression cycles are recognized in the Bulongguoer section of western Junggar. Comparisons of sea level changes among the Bulongguoer section (western Junggar), central Hunan (platform facies of South China), and Euramerica indicate that regional tectonic activities may have played important roles in both western Junggar and central Hunan. In the Palmatolepis rugosa trachytera conodont Zone, sea level rose gradually to the maximum at approximately the Annulata level in the Bulongguoer section, whereas a contemporaneous prolonged lowstand (“Oujiachong regression”) was recognized in central Hunan. The replacement of the Rugaltarostrum Subassemblage by the Ambocoelia? cf. unionensis Assemblage in western Junggar is correlative to the Oujiachong event (the regression and brachiopod diversity decline in South China at the top of Palmatolepis marginifera Zone). During the latest Famennian, the Syringothyris–Spirifer Assemblage replaced the Austrospirifer? sp. Assemblage in western Junggar, as a response to the Hangenberg Event.

New data on fauna and flora of the Upper Paleozoic deposits of the North Siberian platform (Anabar-Khatanga Saddle)

Core hole no. AKh-1 has been drilled within the Anabar-Khatanga oil and gas fields, on the left bank of Khatanga Bay. To date only data on the upper 972.5 meters of the core have been examined in detail and processed by the authors; however, we obtained unique materials displaying lithoand biostratigraphic features of the section of Permian deposits. In the explored part of Permian deposits we can very clearly distinguish the top of the Tustakh Formation and the Lower and Upper Kozhevnikova formations. The assemblages of flora, foraminifers, brachiopods, marine and nonmarine bivalves are characterized and results of palynological analysis are presented.

Palaeobiogeographic patterns of the brachiopod assemblages of the Iberian Subplate during the Late Toarcian–Early Aalenian (Jurassic)

Late Toarcian–Aalenian brachiopod assemblages recorded in different basins located in and around Iberia present a pattern of spatial and temporal distribution which enables two palaeobiogeographic biochoremas to be differentiated: the Iberian-Atlantic District (IAD), which includes the Lusitanian Basin, Asturias and the Basque-Cantabrian Basin, on one hand, and the Iberian-Mediterranean District (IMD); the latter basically comprises the Iberian Range and the Tortosa Platform of the Catalonian Basin. Changes in the composition of the assemblages throughout the stratigraphical interval studied have enabled three main stages characterizing each palaeobiochorema to be recognized. The first two assemblages reflect gradual individualization and isolation, with frequent endemisms. These two stages correspond to the IAD1, IAD2, IMD1 and to the IMD2 assemblages respectively. As from the Pseudoradiosa Chronozone, and during the Aalensis and Opalinum chronozones, an increase in communication between the two districts can be observed, as well as between these and other remote areas. This stage is represented by the IAD3 and the IMD3 assemblages.Some of the brachiopods colonizing the districts are widely dispersed due to their capacity for expansion: they have been found in other Tethysian basins. Other species are exclusive to the district basins and appear to have originated in the areas close to them. For the latter species the existence of two different “evolutionary factories” is proposed: one that supplies species to the IAD, mainly from generic stocks as Neozeilleria, Soaresirhynchia or Praemonticlarella; and another for the species reaching the basins of the IMD, clearly shared by other European and North African basins.The Atlantic “evolutionary factory” remains active until the Aalenian and part of the Early Bajocian, while the Mediterranean is diluted since the Aalenian.

Correction of two Upper Paleozoic stratigraphic units in the Tianshan Mountains region, Xinjiang Uygur Autonomous Region and implications on the Late Paleozoic evolution of Tianshan tectonic complex, Northwest China

The present paper addresses two tectonostratigraphic concerns on the Late Paleozoic Tianshan tectonic complex (TTC), Xinjiang, Northwest (NW) China: (1) stratigraphic succession and age constraint of the Bayingou ophiolite mélange, eastern Tianshan Mountains and (2) timing of closure of the southern Tianshan ocean and accretion of the Siberian craton recorded in the Aiweiergou (AWEG) area, eastern Tianshan Mountains by integrating stratigraphy, palaeontology, tectonopalaeogeography and palaeobiogeography. In the Bayingou area, the detailed palaeontological survey denies the presence of brachiopod Gigantoproductus fauna, typical of the Early Carboniferous faunas in central–south Tianshan complex, in the Anjihai Formation. In contrast, the Anjihai brachiopod assemblage, as a whole, appears to have a high affinity with the Late Devonian faunas of the eastern Junggar Basin, northern Xinjiang, suggesting a Late Devonian age for the Anjihai Formation. The overlying Shadawang Formation yields the Early Carboniferous radiolarians. These two units form the main part of the Bayingou ophiolite mélange, which therefore is likely Late Devonian to Early Carboniferous in age. The Bayingou area has been likely part of the northern Tianshan-Junggar block since the Late Devonian, although it may have been part of the Central Tianshan tectonostratigraphic province prior to the Late Devonian. The topmost strata of the Bayingou ophiolite mélange are characterized by alternation of volcanics, conglomerate and mudstone, and are better re-assigned to the Taoxigou Group rather than the Keguqingshan Formation. The Bayingou ophiolite mélange comprises the Late Devonian Anjihai Formation, the Carboniferous Bayingou and Shadawang Formations, and the Early Permian Taoxigou Group. In the AWEG area, the Permian and Triassic rocks were previously misinterpreted as the Late Permian turbidites and Late Triassic red beds, respectively. In fact, the Permian successions in AWEG consist of the Early Permian Taoxigou Group and early Middle Permian Lucaogou Formation. The former represents a foreland molasse succession, while the latter yields abundant non-marine fossils of plants, bivalves, and gastropods, and represents typical lacustrine facies deposits. The unconformity between the Permian and the Triassic rocks cannot represent the closure of the Tianshan Ocean, but indicates tectonic uplifts in the foreland basins. In contrast, the molasse-type sediments of the Lower Permian Taoxigou Group may have resulted from the post-orogenesis uplifting and mark the closure of the Tianshan Ocean prior to the Early Permian. Thus, the closure of the Tianshan Ocean and the final tectonic accretion of the South Tianshan block might have taken place over the Permo-Carboniferous transition, strengthened by faunal assemblages obtained from both southern and northern sides of the TTC.

Integrated study of fauna and microflora from the Early Devonian (Pragian–Emsian) of northwestern Argentina

The Devonian System in northern Argentina has been broadly analysed, but details of its lithologies, biostratigraphy and fossil content have not been presented in a comprehensive study. We performed the first integrative analysis of the palynological and macrofossil content from the Pescado Formation at the Zenta Range, Argentina. We define a new species of cryptospore and extend the stratigraphic record of the ichnogenus Psammichnites isp. for South America. The stratigraphic ranges of the palynomorphs suggest a time span from the ?late Lochkovian to Pragian–earliest Emsian, but the co-occurrences of key invertebrates narrow the age of the beds to the late Pragian and early Emsian. Moreover, sedimentary analysis indicates a proximal shoreface–foreshore depocenter during this time range for the Zenta region. The contraction phase of the basin during the middle Pragian and Emsian is evidenced by the presence of sand bodies at the top of the column and the higher supply of terrigenous components. During this regression event, a low diversity Malvinokaffric Realm brachiopod assemblage occurs, with dominance of Australospirifer hawkinsi. The predominance of the latter species during this event is coeval with the first decline of the Malvinokaffric Realm in the neighbouring Paraná basin.

A new early Frasnian (Late Devonian) foraminifer from eastern Taurides (Turkey): Evolutionary and paleobiogeographic implications

A complete Devonian sequence is well exposed in the eastern Taurides, forming more than 1000m-thick succession of carbonate and siliciclastic sediments. The carbonate succession, stratigraphically ranging from Middle Devonian to early Late Devonian and mostly comprising limestones, dolomitic limestones and reefal limestones, contains abundant and diverse assemblages of foraminifers, corals, stromatoporoids, calcareous algae, bivalves, brachiopods, ostracods, and conodonts. The limestone samples collected from a more closely sampled stratigraphic section have been investigated for their foraminiferal content. The micropalaeontological analyses carried out on these samples have revealed the presence of an early Frasnian foraminiferal assemblage including predominantly unilocular parathuramminid species and multilocular forms of the genera Nanicella, Paratikhinella and Semitextularia? and further indicated the presence of a new genus and a new species Halevikia deveciae n. gen. n. sp. which appears as an important phylogenetic and stratigraphic transitional taxon between the families Baituganellidae n. fam. and Tournayellinidae, the phylogenetic potentiality of which during the Late Devonian is currently probably underestimated.

Permian sections of southern Primorye: A link in correlation of stage units in the standard and general stratigraphic scales

On the basis of partially published original data on the correlation of Permian sections, the stage boundaries of the standard (SSS) and general (GSS) stratigraphic scales are traced in different paleogeographic regions and climatic belts using reliably substantiated correlation levels. The analysis of the mixed west and east boreal Kungurian–early Ufimian and Middle Permian boreal–peri-Gondwanan–Tethyan brachiopod assemblages from southern Primorye using different stratigraphic methods (biostratigraphy, magnetostratigraphy, event-stratigraphy) and carbon isotope data make it possible for the first time to define five event-correlation levels traceable in remote paleogeographic regions. Presumable analogs of the Sheshma deposits of the GSS Ufimian Stage with the Kazanian biota established in Primorye and traced through the Boreal realm are attributed to the Middle (Biarmian) Series of the Permian System. The magnetostratigraphic method combined with strict biostratigraphic control allows correlation of the Roadian, Capitanian, Wuchiapigian, and Changhsinian stages and their boundaries in the standard stratigraphic scale with the Kazanian, Severodvinian, and Vyatkian stages (and boundaries) in the general stratigraphic scale and with similar units in the Tethyan scale to be specified.

Lower Silurian stratigraphy and brachiopods of the Chingiz range, eastern Kazakhstan

New data on the stratigraphy and faunal assemblages of the Lower Silurian of the Chingiz region are presented. Owing to the discovery of Ruddanian brachiopods in the basal Alpeis Formation, the position of the Ordovician-Silurian boundary has been revised. The stratigraphic range of the Alpeis Formation has been revised to correspond to the range of the Alpeis Horizon in the stratotype and is limited to the beds with the brachiopod Eospirifer cinghizicus and the beds with the graptolites of the Coronograptus gregarius Zone. Beds with Pentamerus longiseptatus of the Donenzhal Horizon are assigned to the Zhumak Formation. A new Ruddanian brachiopod assemblage (ten species) is recognized in the lower part of the beds with E. cinghizicus.

Palaeobiogeographical affinity of the early Pliensbachian (Early Jurassic) brachiopod assemblage of the Northern Caucasus (Russia): A new evidence

Brachiopods are useful in detecting the Mesozoic palaeobiogeographical affinity of European terranes. Numerous representatives of this fossil group known from the lower Pliensbachian deposits of the Northern Caucasus (southwestern Russia) allow quantitative assessment of their palaeobiogeographical affinity. A total of 175 brachiopod species from the Northern Caucasus and several other regions (Bakony, Germany without the Alps, Hallstatt, the Pyrenees, Switzerland without the Southern Alps, the Swiss Southern Alps, and western Algeria) are considered for the purposes of the present study. The relationships between the regional assemblages were examined with three similarity indices, namely the Jaccard Index, the Czekanowski's Quantified Coefficient, and the Gower index. The results indicate the relatively strong similarity of the early Pliensbachian brachiopods of the Northern Caucasus to those of Germany, the Pyrenees, Switzerland, and western Algeria and the strong dissimilarity from the assemblages of the Bakony, Hallstatt, and the Swiss Southern Alps. These results reveal the affinity of the early Pliensbachian brachiopod assemblage of the Northern Caucasus to the Boreal biochore. However, there are Tethyan taxa in this assemblage, and, thus, the latter is of transitional nature. Palaeogeographical and plate tectonic configurations, eustatic fluctuations, differences between the regional depositional environments, etc. may explain the palaeobiogeographical patterns registered in the present study. The regional factors might have been especially important because of the moderate-to-weak global palaeobiogeographical differentiation in the early Pliensbachian. The concept of the Mediterranean microcontinent seems to be also useful for explanation of the early Pliensbachian brachiopod provinciality.

Famennian rhynchonellides (Brachiopoda) from deep-water facies of the Ougarta Basin (Saoura Valley, Algeria)

AbstractIn the Saoura Valley (Ougarta Basin, Saharan Algeria), the lower–upper Famennian part of the essentially shally Marhouma Formation is characterized by deep-water facies and includes horizons rich in ammonoids (goniatites and clymeniids) and blind to eye-reduced phacopide trilobites. They are also rich in small-sized and smooth rhynchonellide brachiopods, investigated here for the first time in order to detail their post-Kellwasser recovery. Rhynchonellides clearly predominate in the brachiopod assemblages (representing 90% of the whole assemblage, with 10 species) composed otherwise of athyridides, orthides and spiriferides. Rhynchonellides are mostly represented by relatively flat leiorhynchids and rozmanariids consistent with poor oxygenation on the sea floor. One new species is described (Evanidisinurostrum saouraensesp. nov.); four genera, previously known only from the south-eastern margin of Laurussia, are reported for the first time from the northern margin of Gondwana: the leiorhynchidSphaeridiorhynchusand the rozmanariidsLeptoterorhynchus, PugnariaandNovaplatirostrum.

Latest Pliensbachian –Early Toarcian brachiopod assemblages from the Peniche section (Portugal) and their correlation

In the present paper we describe the distribution of brachiopods in the proposed Toarcian GSSP (Global Boundary Stratotype Section and Point) at Peniche. We differentiated four assemblages in the stratigraphic interval from the upper Emaciatum Zone of the Pliensbachian to the Levisoni Zone of the Toarcian. Assemblage 1 clearly presents Northwestern European affinities, with many species that are also present in Southern England. In the last levels of the Pliensbachian and in the Mirabile Subzone (the first level of the Toarcian), Assemblage 2 contains taxa that still present Northwestern European affinities, but with a more restricted, even endemic, distribution. The majority of the species in these levels are known from the Iberian Range in Spain and other neighboring basins. An important faunal change takes place in the Semicelatum Subzone, coinciding with the base of the Cabo Carvoeiro Formation, giving rise to Assemblage 3. In this assemblage we observed a clear decrease in the size of the specimens, coinciding with the establishment of the Koninckella Fauna; this fauna is found in several localities in both Northwestern European and Mediterranean areas where the paleoenvironment is relatively deep or poorly oxygenated. Brachiopods disappear in Peniche just above the Polymorphum - Levisoni zonal boundary, as has been observed in several other localities in Western Tethys. Their renewal is marked by the presence of Soaresirhychia bouchardi several meters above the extinction level, constituting Assemblage 4.

Diversity dynamics of Early and Middle Jurassic brachiopods in the Getic and Danubian tectonic units of eastern Serbia: Regional versus global patterns

Quantitative assessment of regional diversity patterns reveals trajectories of faunal development on the basin scale and helps to understand its dependence on palaeoenvironmental changes, global-scale biotic evolution, and major events in the history of the Earth. A total of 86 species, 50 genera, 18 families, and 9 superfamilies of Early and Middle Jurassic brachiopods are established in the Getic and Danubian tectonic units of eastern Serbia. Compilation of their stratigraphic ranges allows analysis of their total diversity, number of appearances and disappearances, and turnovers. In both units, brachiopods radiated rapidly in the Early Pliensbachian. Then, their diversity declined, and these fossils disappeared. A new radiation took place in the Late Bajocian, and brachiopods remained diverse until the end of the Bathonian. They disappeared before the Callovian in the Getic Unit and in the Early Callovian in the Danubian Unit. The Early Pliensbachian radiation was significantly stronger than the Late Bajocian at the level of species; the strength of these radiations was more or less comparable at higher taxonomic levels. The strength of turnovers among brachiopods differed through geological time. The composition of the Middle Jurassic brachiopod assemblages was more or less stable. Regional shoreline shifts, basin depth changes, palaeobiogeographical changes, and plate tectonic re-organizations were possible controls on regional patterns of brachiopod diversity dynamics. However, the latter also reflects some diversity patterns documented globally and in some other regions (the Bakony Mountains, the Swiss Jura Mountains, and the Northern Caucasus).

A Middle Ordovician (Darriwilian) Dysaerobic Brachiopod Assemblage from the Precordillera Terrane of Argentina: Implications for Early Colonization of Deep Waters

A rapid increase of water depth associated with dysoxic bottom conditions took place in the central part of the Precordillera basin during the middle Darriwilian. The peak of transgression and drowning of the carbonate ramp are marked by the transition from the uppermost carbonate beds of the San Juan Formation to a rhythmic alternation of graptolitic black shales and marlstones (base of the Los Azules Formation). This lithofacial change is associated to a drastic faunal shift involving a renewal of the ecologic structure. The carbonate facies dominated by filter-feeding organisms were rapidly replaced by new communities characterized by benthic and pelagic trilobites and low-richness assemblages of minute brachiopods. Two main associations are recognized in the Los Azules Formation: a basal ephemeral Sivorthis-Mendolaspis Association and a more persistent Chilcorthis-Palaeoglossa Association inhabiting deeper and more dysoxic sea-bottoms. The new plectorthoid family Chilcorthidae is established to include the new genus Chilcorthis. Five new species are described: Palaeoglossa minima sp. nov., Cyrtonotreta vasculata sp. nov., Philhedra pauciradiata sp. nov., Sivorthis precordillerana sp. nov., and Bockelia canalis sp. nov. Associate taxa are Anomaloglossa? sp., Cyrtonotreta? sp., Protohesperonomia? sp., Syntrophia? sp. and unidentified Finkelnburgiidae, Polytoechiidae and Aegiromenidae. The first successful deep-water incursions are Floian—Dapingian in age, but from the Darriwilian they have been documented in several paleoplates. These pre-Sandbian brachiopod communities were more restricted geographically than the global Foliomena Fauna with which they share some taxa and similar morphotypes but differ in the higher proportion of linguliform brachiopods and less diverse plectambonitoids.

Late Ordovician and early Silurian brachiopods from the Zagros Ranges, Iran

ABSTRACTBrachiopods are among the most common components of the Late Ordovician benthic faunal assemblages recorded in the Faraghan Mountains, Zagros Ranges, Iran. A total of 19 species referable to 16 genera are identified, including seven new species; namely Drabovia elegans, Hibernodonta bonehensis, Hedstroemina zakeenensis, Jezercia faraghani, Protomendacella multicostata, Tafilaltia dargazensis and Tafilaltia seyahouensis. Reported brachiopod assemblages are oligotaxic (2–3 species per assemblage) to monotaxic. The only exception is the medium diversity Aegiromena-Hedstroemina Association, with up to ten species, which occurs at the lower part of the A. nigerica Zone. Low diversity patterns were probably controlled by the palaeogeographical position of the region in high southern latitudes throughout the Ordovician. Paterula sp. and Iranospirifer sp. are the only brachiopods documented from the Silurian (Llandovery) Sarchahan Formation. This paper gives the first detailed report of shelly fossils from the Llandovery ‘hot shale’ of the Arabian margin of Gondwana. Most of the Katian genera, and many of their species, are shared with neighbouring high- to mid-latitude peri-Gondwanan margins, including Morocco, Spain, France, Sardinia and Bohemia.

First glimpse into Lower Jurassic deep-sea biodiversity: in situ diversification and resilience against extinction.

Owing to the assumed lack of deep-sea macrofossils older than the Late Cretaceous, very little is known about the geological history of deep-sea communities, and most inference-based hypotheses argue for repeated recolonizations of the deep sea from shelf habitats following major palaeoceanographic perturbations. We present a fossil deep-sea assemblage of echinoderms, gastropods, brachiopods and ostracods, from the Early Jurassic of the Glasenbach Gorge, Austria, which includes the oldest known representatives of a number of extant deep-sea groups, and thus implies that in situ diversification, in contrast to immigration from shelf habitats, played a much greater role in shaping modern deep-sea biodiversity than previously thought. A comparison with coeval shelf assemblages reveals that, at least in some of the analysed groups, significantly more extant families/superfamilies have endured in the deep sea since the Early Jurassic than in the shelf seas, which suggests that deep-sea biota are more resilient against extinction than shallow-water ones. In addition, a number of extant deep-sea families/superfamilies found in the Glasenbach assemblage lack post-Jurassic shelf occurrences, implying that if there was a complete extinction of the deep-sea fauna followed by replacement from the shelf, it must have happened before the Late Jurassic.

The Upper Homerian (Silurian) machaerid sclerite from Lithuania

Machaerids are a branch of Lophotrochozoans closely related to the Annelids known from the Early Ordovician to the Mid Permian marine environments. One specimen of machaerid sclera was found in the Viduklė-61 well, Siesartis Formation, at the depth of 1 285.1 m. Along with the specimen, the graptolite species of Colonograptus deubeli (Jaeger) was found, which is a mark of the Late Homerian, Gėluva Age. Brachiopod fauna shows that at this time there was an anaerobic, low turbulence and low shelf marine environment, i. e. BA 4–5 zone of the benthic brachiopod assemblage. Machaerid studies have shown that it belongs to the Plumulites genus. Without a full animal print with all sclerites we cannot accurately describe these fossils. This is the first specimen which was found in Lithuania, Gėluva Regional Stage. This finding will give more information about fauna recovery after extinction in the Early Gėluva Regional Stage, also known as the ludgreni Event. With the help of machaerid findings, we also could reconstruct palaeoenviroments and autecology.

Post-Glacial Hirnantian (Upper Ordovician) Bryozoans from Western Argentina: Implications for Survival and Extinction Patterns

Abstract. Two bryozoan taxa occurring in the Hirnatian (Upper Ordovician) deposits in western Argentina document a first postglacial community associated with a mid-to high-latitude brachiopod assemblage, known as the typical Hirnantia fauna, in the Argentine Precordillera. Helopora fragilis Hall and an indeterminate phyloporinid occur within a thin but conspicuous shell bed that overlies diamictitic deposits from the lower member of the Don Braulio Formation. The abundance of well preserved specimens of bryozoans together with the dominance of suspension feeders suggests a mid-shelf setting (offshore transition) with an intermediate to low sedimentation rate, low turbidity, and nutrient-rich conditions. Hirnantian bryozoan assemblages identified from tropical and subtropical regions are rather rare, and this assemblage represents the first high-latitude Hirnantian record. The low diversity of bryozoans may be related to high-latitude location of Argentina during the Late Ordovician. Helopora Hall occurs ...